Shielded spark plug



Dec. 19, 1933. RABEZZANA 1,940,325

SHIELDED SPARK PLUG Filed April 4. 1932 III 190201 fiaezzana 3% M WYPatented Dec. 19, 1933 SHIELDED SPARK PLUG Hector Rabezzana, Flint,Mich, assignor to A 0 Spark Plug Company, Flint,

0! Michigan Mich a company Application April 4, 1932. Serial No. 602,8923 Claims. (01.123-169) This invention relates to ignition systems forinternal combustion engines and particularly to improvements in sparkplugs.

It is a primary object of the invention to provide a spark plugespecially adapted for use on an engine which is to be operated in thevicinity of radio apparatus, and which plug, in its preferred form,incorporates as a part of the ground-' ed shell an integral extension orskirt enclosing the outer portion.of the insulator core and centralelectrode, and serving as a support and.

ground connection for a shield surrounding current conducting cableleading to the plug. With the arrangement provided, radio apparatusnear, by is shielded from electrical radiations incidentv to theoperation of the ignition system and which otherwise would interferewith communication. An important feature of the integral struc-' ture isthe absence of any hindrance to the tree heat flow from the shell intothe engine block. That is, the heat from the shell is transferredthrough the customary sealing gasket directly to the block withouthaving to pass through any intermediate body such as a separate coreshield formed independently of the plug proper and interposed betweenthe shell and block. It also aids materially in reducing costs.

The invention includes certain structural details all to be describedhereinafter in connection with various embodiments illustrated in theaccompanying drawing, wherein Figure 1 is a vertical sectional view ofone type of plug and cover; Figure 2 is an elevation with parts insection to show the application of the invention to another type ofplug; Figures 3 and 4 are sectional views illustrating alternativeassemblies, and Figure 5 is a detail perspective view showing one of theretainer parts assembled in'the plug structure of Figure 4.

Referring to the drawing, the central core as- I sembly includes aninsulator 1 of porcelain or the like, surrounding a central electrodeand having intermediate its ends an enlargement 2 positioned within aninner metal shell 3'having at opposite ends inwardly extending flanges 4and 5, respectively, providing seats {or the shoulders afforded by theenlargement 2. Sealing gaskets 6 and 7 are preferably interposed betweenthe shoulders and retainer flanges to prevent leakage. The ,assembly ofthese parts is preferably completed by first inserting the core in theinner'shell and then bending inwardly the flange 5 from a previousupstanding position. This inner shell is threaded into an outer shellbody 8 v for engagement within a spark plug opening in the wall 12 ofthe engine combustion chamber. From the opposite end of the plug body 8extends an enlarged cylindrical portion or skirt 13 surrounding theouter portion of the core 1 and having on its exterior a series ofperipheral ribs or cooling fins 14. These cooling fins assist in.

the dissipation of heat, although most of the heat is transferred to thewall 12 in the usual fashion.

Seated on the upper end of the skirt 13 is a cover or cap 15, preferablymolded of bakelite, hard rubber or the like, and provided on itsexterior with a metallic coating or covering 16, preferablyelectro-deposited, which extends over the seat portion of the cover andin contact as'at 17 with the skirt l3. Embedded in the top of the coveris armetal seat 18 having a depression that receives a ball or roller 19carried by a swinging bail 20 which is pivotally carried by the sparkplug shell, as is most clearly shown in Figure 2, whereby to securelyand detachably hold the cover in position over the outer end of theskirt. Within the cover 15 is formed a passageway 21 for the receptionof an end of an insulated current conducting cable 22, forming a part ofthe engine ignition system. The cable 22 is held in place by means of ascrew stud or keeper 23 extending from the inside of the cap and havinga conical outer end extending into the opening 21, piercing the cableinsulation and contacting with the current conducting wires. The screwstud 23 also serves as a mounting for the coil spring 24 contacting withthe terminal head 25 of the central electrode for the passage of currentfrom the cable 22 to the spark plug. At the outer end of the passageway21 the cover is provided with a integral skirt 13 projects outwardlyfrom the.

outermost portion of the shell proper, it will be obvious that the readytransference to the wall 12 of heat taken up by the plug parts isunchecked thereby.

The application oi the shielding to the so called mica plug isillustrated in Figure 2 where the cover 15 is mounted on the outer endof the skirt or cylindrical extension 30 of the metal shell 31, and theshell screw threadedly receives the gland 32, forming a part of the coreassembly between the mica bodies 33 and 34, which surround and insulatethe central electrode.

Instead oi proviidng a separate retainer shellfor the insulator core,the core may be permanently secured in the shell proper, as illustratedin Figure 3', where the central opening or bore 01' the shell 35receives the central enlargement 36 or the insulator core 37 and theshell is provided initially with an upwardly extending lip 38, which isbent inwardly and over the enlargement 36 to retain the core in theshell.

'In lieu of the integral lip just referred to, the structure shown inFigure 4 may be employed to removably retain a core enlargement 39 inthe shell 40. Here the skirt or shell 41 is provided with an annulargrove 42 on its interior surface to receive a split ring 43 which formsa bearing for a retainer collar 44. The inner margin of the collar 44,as shown particularly in the detail view, Figure 5, forms a circularseat 45 for the core enlargement 39, and irom the seat 45 the collarextends angularly upwardly with portions cut away at spaced intervals topresent a series of spring fingers 46. The assembly and removal of theparts involves merely the manipulation of the split ring retainer intoor out of its seating groove to either hold the parts in the relationshown in the drawing or permit their separation.

I claim:

1. In the ignition system of an internal combustion engine, a spark plughaving inner and outer sub-assembly units, said inner sub-assemblyincluding an insulator core surrounding an electrode and having mountingmeans intermediate its ends, and said outer sub-assembly having as aunitary structure an intermediate portion to mountably receive themounting means or the inner assembly, a skirted portion receivablewithin an engine spark plug opening and provided outer sub-assemblyunits, said inner assembly including as an integral part thereof anexteriorly threaded gland, and said outer assembly comprising a metallicshield having an exteriorly threaded end portion carrying a groundelectrode, an interiorly threaded intermediate portion to receive saidgland oi the inner assembly and an integral shielding portion in spacedrelation to the inner assembly to receive and ground therethrough aterminal of a shielded cable.

3. In the ignition system of an internal combustion engine, a spark plughaving an insulator core surrounding an electrode and having anintermediate shouldered portion, a shielding shell carrying a groundelectrode near one end and having a counterbored intermediate portion toreceive the shouldered portion of the core, together with a shieldingportion surrounding the upper end of the core, and means to hold theshouldered core portion in the counterbore oi the shell including aretaining ring engaging the shoulder and a snap ring bearing for theretainer removably engaging a seat in said shielding portion.

HECTOR RABEZZANA.

